Fourteen isolates of bacteria resembling Streptococcus sanguis have been obtained from the supragingival plaque of the monkey (Macaca fasicularis. The bacteria were identified by their enzyme activity, fermentation of sugars and production of glucan from sucrose. By use of fluorescent antibodies, specific for S. sanguis biotypes 1 and 2, all but one of the isolates appear to be biotype 1. Secretory IgA has been purified from human colostrum by column chromatography and an IgA1 paraprotein from serum by HPLC. In addition, pools of colostrum and serum have been collected from M. fascicularis in order to obtain purified monkey 11S and 7S IgA. The S. sanguis isolates appear capable of cleaving human IgA1 paraprotein as determined by cellulose acetate zone electrophoresis, immunoelectrophoresis and SDS polyacrylamide electrophoresis. The patterns of cleavage appear to differ from S. sanguis 10556.